Line an 8 x 8-inch (20 x 20 cm) baking pan with parchment paper and set aside.
In a large bowl, combine the rolled oats and protein powder and stir until evenly mixed.
In a microwave-safe bowl, add the peanut butter and honey (or brown rice syrup). Microwave in 20-second intervals, stirring between intervals, until the peanut butter softens and the mixture is smooth and thick.
Pour the warmed peanut butter mixture into the dry ingredients and mix until fully combined. If the mixture is too thick, add a few tablespoons of water to loosen it.
If using chocolate chips, fold them in until evenly distributed.
Transfer the mixture to the prepared pan and press it firmly and evenly into the pan with a spatula or the back of a spoon.
Refrigerate for at least 1 hour to firm up, then remove from the pan and slice into 20 bars.